1. Field of the Invention
This invention relates to a trolley pole assembly and more particularly to a trolley pole having a hollow construction for housing an electrical conductor in a protective enclosure extending from the connection of the conductor to the trolley wire at one end and to a propulsion motor at the opposite end.
2. Description of the Prior Art
It is well known, in underground mining operations, to utilize electrically propelled vehicles, such as locomotives, jeeps, portal buses and the like, having a trolley pole connection between an overhead trolley wire and the propulsion motor on the vehicle. Direct current is supplied from the overhead trolley wire to an electrical conductor supported by the trolley pole. The conductor extends along the trolley pole into electrical connection with the propulsion motor on the vehicle. For many years, it was the conventional practice to utilize solid wooden trolley poles for feeding the conductor from contact with the trolley wire to the propulsion motor. More recently, the use of trolley poles fabricated of an electrically insulated material, such as filament-wound fiberglass reinforced plastic, has been adopted in which the trolley pole has a hollow construction for feeding the conductor down through the trolley pole as opposed to supporting the conductor externally on the trolley pole.
U.S. Pat. No. 4,116,312 discloses a hollow fiberglass trolley pole which contains the electrical conductor and a fuse case so as to enclose the conductor and seal it from the deleterious effects of moisture, corrosion and breakage. The conductor is positioned in the pole and is connected to one end of a fuse which is also contained in the pole. The opposite end of the fuse is connected to another electrical conductor that extends out of an opening in the side of the pole. From the pole, the electrical conductor extends to an electric motor that drives the vehicle on which the pole is mounted. The pole is mounted in a socket on the vehicle.
U.S. Pat. No. 1,867,480 discloses a trolley pole made of flexible, insulating material, such as rubber, which permits bending of the pole, when the pole strikes an obstruction. The pole includes a longitudinal passageway for receiving the conductor. The conductor enters the pole through an opening at the upper end portion of the pole, and the wire exits the pole through an opening at the lower end of the pole. With this arrangement, the pole forms an insulating housing for the conductor, but the conductor is nevertheless still exposed at the upper and lower ends of the pole.
U.S. Pat. No. 2,265,018 also discloses a trolley pole construction that includes, in one embodiment, a thin-walled, tapered, metallic tube, having a hollow reinforcing core of wood in which the electrical conductor is positioned. The pole is positioned in a socket of a base mounted on the vehicle. The conductor extends downwardly through the insulated core and out through the lower end of the socket. The conductor is exposed as it extends to the propulsion motor of the vehicle. Further embodiments of the trolley pole illustrated in U.S. Pat. No. 2,265,018, include an external rather than internal reinforcing member fabricated of a resilient material around the trolley pole.
U.S. Pat. No. 2,644,862 discloses a trolley pole insulating material that includes a covering of cotton impregnated with rubber or plastic material or, in the alternative, a protective coating of liquid plastic material, such as polyethylene to the outer surface of a trolley pole tube to provide a weather-resistant coating around the pole.
U.S. Pat. Nos. 699,927; 1,468,265; 1,743,300; and 1,787,013 also disclose trolley poles of a tubular construction in which the electrical conductor passes through the trolley pole.
There is need for trolley pole apparatus which provides a sealed path for the conveyance of the electrical conductor from the contact shoe through the trolley pole and from the end of the trolley pole to the point of electrical connection of the conductor to the propulsion motor. While it has been suggested to position the conductor within an electrically insulated trolley pole, the prior art devices do not provide a sealed path for the electrical conductor that extends along the entire path from the contact shoe to the connection at the propulsion motor. With the known arrangements, the electrical conductor is exposed to the effects of moisture and is subject to physical damage. Therefore, there is need for a trolley pole assembly in which the electrical conductor is maintained in a protective enclosure from the point where the conductor passes out of the trolley pole to the point of connection to the propulsion motor.